The present invention relates to an improved trailer unit having a breakage resistant frame construction of enhanced strength. The trailer unit is particularly well adapted for carrying concentrated heavy loads such as construction rock.
Trailers for carrying extremely heavy materials have been available for a long period of time. These are generally constructed in one of two ways. Either the load is concentrated over a single double axle wheel unit or the body is constructed so as to distribute the load between two relatively closely spaced double axle wheel units. The dual rear axle of a truck or tractor may or may not serve as the forward wheel set. A vehicle of the second type is shown in U.S. Pat. No. 2,912,253, to Harris et al. This is an example of a trailer designed to support a heavy load between the front and rear axles of a trailer unit. In this case, a trailer frame in the form of an inverted gable-type truss serves to prevent deflection at the midpoint of the trailer bed. U.S. Pat. No. 4,289,353, to Merritt, is a somewhat similar example in which the rear wheels of a tractor form the forward load carrying wheels of the trailer. U.S. Pat. No. 3,310,345, to Rowden, employs a load suspension plan similar to that of Merritt. With the exception of the Harris et al. trailer, all of the aforementioned units are designed for relatively high attachment to the prime mover through the well known "fifth wheel" type of coupling.
In the case of trailers designed for carrying heavy construction rock, rubble or dirt, a very low coupling point is usually desirable. This is necessitated because the prime mover itself normally carries a dump body and clearance must be provided above the trailer tongue for the tailgate to swing open when the load is dumped. The patent to Breazeale et al., U.S. Pat. No. 3,771,829, shows one example of how this problem can be accommodated. The Breazeale et al. frame is inclined from a low hitch point to a higher load supporting point. The trailer dump body itself is equipped with two wedge-shaped filler pieces so that it assumes a horizontal attitude when resting on the frame members. The frame of the Breazeale et al. trailer consists of two conventional pieces of channel iron which diverge from an apex point.
A somewhat similar arrangement is shown in French Pat. No. 1,122,388. Here, the front of the trailer is supported on a simple post attached to a cross member on the sloping frame.
Hribar, in U.S. Pat. No. 3,193,330 supports the dump body on a conventional frame which is tied to the prime mover by a truss formed as a three-sided pyramid. A similar arrangement is shown in U.S. Pat. No. 3,082,039, to Clement.
Trailers of the type described usually have a long tongue or other means for separating them widely from the prime mover. This is done in order to minimize weight concentration on the highways. The long coupling mechanism introduces another problem, however. Because of the great distance from the support point at the coupling, the bending moment acting on the frame at the forward end of the load can be very severe. This induces a high stress concentration which has been a frequent cause of frame breakage.
The present invention has overcome the above problem by using an improved frame design which resists deflection at high stress concentration points yet is accommodative of the required low coupling position to the print mover. Further it allows the load carrying body to bear directly on the frame without the use of filler pieces or similar supports.